Four basic methods have been used in the past to sterilize medical instruments which are retained within sterilization trays during sterilization operations. These methods include using (1) ethylene oxide (EO); (2) chemical soaking; (3) steam sterilization; and (4) plasma sterilization employing a hydrogen peroxide (H.sub.2 O.sub.2) vapor.
The sterilization method using the ethylene oxide includes using a highly flammable and toxic gas which therefore require special precaution. Further, this sterilization technique requires a long time to complete. Thus, expensive medical instruments cannot be rapidly sterilized and used many times in a day. An advantage this method has over others is that sterilization occurs at a low temperature. However, overall this particular technique is expensive and is in disfavor.
The second method utilizes chemical soaking to sterilize instruments. This sterilization method can occur at low temperatures. However, the soaking generally takes a long time and therefore is undesirable. Further, the chemicals used to do the sterilization are often considered to be hazardous and require special handling and disposal.
The third method is steam sterilization. Instruments are placed within a sterilization tray and loaded into a sterilization device such as an autoclave. Using a combination of steam, time, temperature and pressure, the instruments in the autoclave are sterilized. An advantage to this particular method is that it is fast and cheap. However, the requirement of high temperature requires that sterilization trays be stable when placed in a high temperature environment for an extended period of time. That is, the sterilization tray should have a high heat deflection value, i.e., little deformation and dimensional change due to the extended heating.
Metal sterilization trays are quite good at retaining their shapes during high temperature sterilization. However, as many medical instruments are made of metal and are extremely expensive, the instruments are susceptible to being accidentally banged or scraped against the metal sterilization trays, thus damaging the medical instruments. Therefore, it is preferable that plastic sterilization trays be used. Currently, the plastic of choice for sterilization trays used in steam sterilization is Radel 5000. The Radel 5000 provides the desired heat deflection characteristics during extended high temperature sterilization cycles. Unfortunately, Radel 5000 is a relatively expensive material.
The newest of the above sterilization techniques is using a plasma which employs hydrogen peroxide (H.sub.2 O.sub.2) as the sterilization agent. The advantage this particular method offers is that sterilization can occur at a relatively low temperature and with a relatively short time cycle. The short time cycle is important in the event that expensive instruments are to be used several times in a day. Unfortunately, sterilization trays made out of the Radel 5000 readily absorb the hydrogen peroxide. This absorption is undesirable because it often causes the machinery used in the plasma sterilization to shut down. Further, the absorbed hydrogen peroxide may later release from the sterilization trays and into the medical instruments or atmosphere which is undesirable.
Sterilization trays made of plastics other than Radel 5000 have been made for use in hydrogen peroxide plasma sterilization devices. However, these sterilization trays typically do not have sufficient heat deflection values to adequately withstand the temperatures of steam sterilization.
The present invention intends to overcome many of the shortcomings of the above described conventional sterilization trays.